This invention relates to a self-lubricating bearing material and particularly to a bearing material comprising a low friction polymeric resin such as polytetrafluoroethylene (PTFE).
One type of existing bearing material is in the form of a tape. PTFE is mixed with fillers such as bronze powder, moly-disulfide, graphite, carbon, chopped glass fibers or the like to improve the strength and wear rate of the PTFE. The mixture is pressed into a billet which, after being sintered and cured, is skived into a tape. The tape may be etched and then adhesively bonded to a backing to improve the mechanical properties of the bearing material. The load carrying ability of a bearing formed from such material is limited by cold flow or deformation of the skived tape and typically is in the neighborhood of 10,000 psi. at a low velocity of one surface foot per minute.
Another type of bearing material is made by sintering a thin layer of bronze powder to a copper plated steel strip and by coating the strip with a mixture of PTFE and lead. The finished strip is rolled into a journal bearing. Such a bearing (commonly known as a DU bearing) has a high load carrying capacity (e.g., approximately 50,000 psi. to a low surface velocity) but has a very thin wear surface since only a thin overlay of PTFE may be placed on the metal strip. Moreover, a steel strip which is thicker than about 0.120" is difficult and expensive to roll into a bearing and thus the thickness of the bearing is limited. The lead which is mixed with the PTFE presents a health hazard.
In yet another type of bearing material, a wire mesh screen, typically phosphorus bronze, is laminated with a skived PTFE composite tape. The lamination is effected by heat and pressure and sometimes with an adhesive which has an affinity for PTFE. The bearing material is of poor quality since there is only limited attraction between the PTFE tape and the wire mesh. Adhesives are not very effective since they bond only to the etched PTFE surface of the tape, the etched surface being disrupted when the tape is pressed onto the wire mesh.
Wire mesh also is used in another type of bearing material. In this instance, the wire mesh is impregnated with PTFE resin and is covered with a thin overlay of resin which is sintered in place. The resulting bearing has a thin wear surface. To create a high load carrying capacity, it is necessary to adhesively bond the PTFE/mesh layer to a metal or fiberglass backing. The integrity of the bearing material is limited to the strength of the adhesive bond and, since PTFE is difficult to bond to metal or fiberglass, the bearing material is relatively low in strength. Moreover, it is not feasible to use a continuous process to press resin with a high concentration of fillers or with fillers of large particle size into an unsupported wire screen.